SEOUL, March 21 (Reuters) - Ousted South Korean President Park Geun-hye apologised to the country on Tuesday as she arrived at prosecutors' offices for questioning as a criminal suspect in a widening corruption investigation that has already cost her the presidency.

"I am sorry to the people. I will faithfully cooperate with questioning," Park said in front of media at the steps of the office building, in her first comments directly to the public since she was dismissed on March 10.